Genus Latrodectus - Widow Spiders
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Chelicerata (Chelicerates)
Class Arachnida (Arachnids)
Order Araneae (Spiders)
Infraorder Araneomorphae (True Spiders)
No Taxon (Entelegynae)
Family Theridiidae (Cobweb Spiders)
Genus Latrodectus (Widow Spiders)
Other Common Names
Widow (Black Widow, Brown Widow, Red Widow)
Explanation of Names
is basically Greek for 'biting in secret'. For further, more specific details, refer to (1)
Latrodectus breaks down taxonomically into approximately 31 recognized species, five (5) of which are found in the United States; four (4) species are native, one (1) species (L. geometricus) was introduced.
Latrodectus spiders are the largest of the Theridiidae (cobweb weaver) spiders. The size of a Latrodectus can vary across species. Please refer to specific species for more information. But in general...
Adult females: 1/2-inch long, not including the legs (about 1-1/2 inches when legs are spread).
Adult male: About half the female’s size, with smaller bodies and proportionally longer legs.
Adult female hourglass variation is somewhat inconsistent regarding North American species.
L. geometricus, which doesn't even belong in the US, is the only 'NA' species with basically 'no' (I haven't seen them all, and there are always exceptions, maybe an unknown population somewhere in the world with a unique hourglass shape or color) hourglass variation in females, with the exception of color, ranging from red to orange. Male hourglasses do show variation in color and shape, but hourglass unnecessary for aid with ID.
L. mactans, hesperus, variolus, and bishopi females have hourglass variation, from complete to absent. Many of these spp. variations are represented on Bugguide.
L. hesperus - hourglass primarily complete, typical hourglass shape, anterior and posterior halves often proportional, posterior half (next to spinnerets) equal to but 'never' wider than anterior half when hourglass complete.
Hourglass marking may be complete, split*, partial*, or absent. Adult male hourglass primarily complete.
L. mactans - hourglass primarily complete, posterior half (next to spinnerets) 'always' wider than anterior half when complete.
Hourglass marking may be complete, split*, partial*, or absent. Adult male hourglass primarily complete.
L. variolus - hourglass primarily split or partial, when complete anterior and posterior halves generally proportional. Hourglass often split in middle, with both halves or one half prominent to reduced, or hourglass is partial (anterior or posterior half absent) with either posterior or anterior half prominent or reduced, or hourglass is completely absent. Adult males show same hourglass variations as adult females.
L. bishopi - hourglass primarily partial* or absent, sometimes split*, rarely complete. Adult males show same hourglass variations as adult females.
*see variolus description
An important characteristic of the Latrodectus is its “comb foot.” The spider has a row of strong, curved bristles on the hind pair of legs, which form a distinct comb. The comb is used for flinging silk over its prey.
Female: The coloration of the spider can vary by species (brown, black, red), but all females (of the species found in the United States and Canada) are shiny black, brown-black, or red with possibly a row of red spots on the top of the abdomen along the midline. Two reddish triangles resembling an hourglass are present on the underside of the abdomen of all species except the Red Widow (L. bishopi). Females are sedentary, staying on or near their web. They will bite if molested.
Male: Adult males are harmless. The male’s abdomen usually has red spots along the upper midline and white lines or bars radiating out to the sides. (The number of bars can indicate which species.) Males almost exclusively wander in search of females.
Immatures: Immatures of both genders are harmless. Newly hatched spiderlings are predominately white or yellowish-white, gradually acquiring more black and varying amounts of red and white with each molt. Juveniles of both sexes resemble the male and are harmless. The males will mature faster, causing the spider to maintain more of its juvenile coloration; whereas females mature slower, allowing the spider to obtain the darker, shinier appearance. (See Life Cycle section for more information.)
These spiders are nocturnal and build a three-dimensional tangled web, often with a conical tent of dense silk in a corner where the spider (female) hides during the day.
There are five species of Latrodectus in North America, which can generally be identified by location, markings (style of hourglass), sometimes coloration. (Click the taxonomical name to go to corresponding species information guide page).
Southern Black Widow
: (L. mactans
) Southern black widows have a longer than wide second orange spot on the abdomen
Northern Black Widow
: (L. variolus
) Northern black widows have a wider than long 2nd orange spot
Western Black Widow
: (L. hesperus
: (L. geometricus
Throughout the United States and Southern Canada. It is more common in the southern and western US states.(2)
Black Widows are not found on the mainland of Northwestern Washington. There have been a few populations recorded from Whidbey Island and some of the San Juan Islands.
In nature, it is a fairly common spider; most species are found in recesses under rocks, or logs in a woodpile, in crevices or holes in dirt embankments, in dark sheltered spots, and in barns & outbuildings, where it builds strong-walled retreats quite close to the ground.
However, they readily adapt to human-altered environments, and are most commonly found in outbuildings (sheds, barns, privies), water meter holes, nursery cans, around lids of dust bins, around seats of outdoor privies, spaces under chips of wood, around stacked materials of any kind, in deserted animal burrows or rodent holes, entwined in grape arbors, and under any item or structure (e.g., barbeque grill, slide, sand box) that has been undisturbed for a lengthy period. Additionally, in the eastern United States, Latrodectus mactans is associated with littered areas, with dumps of large cities, with garages, and storage sheds. In arid parts of Arizona, this spider inhabits almost every crevice in the soil and its nests are found in cholla cacti and agave plants. (Net Ref. 1
This spider may also find its way into clothing or shoes and occasionally seeks a spot in a house to build a web, but it is usually not found indoors. When it does seek shelter in a building, it is due to cold weather and a need for a dry shelter.
For the Red Widow, the webs are generally located 3' to 10' above the ground, (spiderlings and immatures build their webs close to the ground) and the main area of the web can extend up to 4' from the females retreat. It is basically a cobweb sheet with a large number of snare lines extending upwards. Their prey flies into these snares, and usually falls to the sheet. The widow then rushes out to make the capture.
They typically prey on a variety of insects, but occasionally they do feed upon other arachnids. When the prey is entangled by the web, the spider quickly comes out of its retreat, punctures and poisons its prey. The poison takes about 10 minutes to take effect, meanwhile the prey is held tight by the spider. When movements of the prey cease, digestive enzymes are released into the wound . The black widow spider then carries its prey back to its retreat before feeding. (3)
Black widows mature in two to four months. At first the young appear white or yellowish, but with each molt their coloration darkens. Until maturity both sexes resemble the male and are harmless to humans. Females usually mature within 90 days, and live for another 180 days, while males usually mature about 70 days and live only about a month longer. Males generally require fewer molts to mature than females.
Female black widows commonly lay about 400 (occasionally up to 900) eggs in oval, papery sacs, about 1/2 inch long. A single female can produce nine egg sacs in a summer. Eggs incubate for 20-30 days, after which the spiderlings hatch; however, more than 12 rarely survive this process, due to cannibalism.
The female black widow's notorious habit of eating the male after mating is a misconception, but there are observed cases where the female will consume the male during or after mating. This behavior has actually been observed in many species of spiders other than just widows. Females are nocturnal, shy and rarely leave their web, from which they hang, belly upward. Males and females feed on insects and other arthropods and are preyed upon by mud-dauber wasps. (Net Ref. 2
Caution: Widow spiders (Latrodectus spp.) are venomous, and can be harmful to people.
Latrodectus spp. bites occur most frequently when the spider is trapped against human skin, either by reaching under objects where the spider is hiding or when putting on clothing, gloves or shoes containing the spider. Widow spiders are generally very timid and only bite in self-defense when they accidentally contact humans. The bite from the widow spider causes a set of symptoms in the bite victim known collectively as latrodectism. Latrodectism is caused by the neurotoxic venom injected by the widow.
The severity of a Latrodectus bite varies with the species, the age and health of the victim, and the amount of venom injected into the victim. The most severe bites have been reported to be from the Southern Black Widow (L. mactans). The Brown Widow (L. geometricus) is suspected to have the least severe bite (it is considered to possibly be medically insignificant). It is suspected that the brown widow either is more hesitant to bite, or the amount of venom injected (a process called envenomation) is less than the amount injected by its cousins.
For the most part, the black widow's bite may be felt only as a pin prick, during which the spider's fangs inject a minute amount of highly toxic venom under the skin. The severity of the victim's reaction depends on his or her age and health, and on the area of the body that is bitten. Local swelling and redness at the site may be followed in one to three hours by intense spasmodic pain, which can travel throughout the affected limbs and body, settling in the abdomen and back (intense abdominal cramping, described as similar to appendicitis), and can last 48 hours or longer. Elderly patients or young children run a higher risk of severe reactions, but it is rare for bites to result in death; only sixty-three having been reported in the United States between 1950 and 1959 (Miller, 1992). Other symptoms can include nausea and profuse perspiration. If left untreated, tremors, convulsions and unconsciousness may result. When death does occur, it is due to suffocation.
Note: Male Lactrodectus spp. spiders (and the juveniles of either gender) do not bite and are not dangerous; only bites from the adult female present a medical concern.
If you are bitten by a widow. spider:
Contact your physician, hospital or poison center immediately and follow their instructions. Poison Centers across the country now have a new national emergency phone number - 1-800-222-1222.
Collect the spider if possible for identification. Your physician may administer an antivenom treatment and calcium gluconate to alleviate pain, and will probably treat the site with antiseptic to prevent infection.
If you have a heart condition or are otherwise vulnerable, you may require a hospital stay until symptoms subside. Usually bite victims recover fully within two to five days.
Be very careful when working around areas where widow spiders may be established. Take proper precautions-wear gloves and pay attention to where you are working. The reaction to a widow bite can be painful, and the victim should go to the doctor immediately for treatment.
Miller, T. 1992. Latrodectism: Bite of the Black Widow Spider. Am. Fam. Phys. 45:181
Please refer to the "Works Cited" Section
Animal Diversity Web
: An excellent site about Widows, especially the Southern Widow (L. mactans)
Venomous Spiders in Florida
: A detailed article by G. B. Edwards, Taxonomic Entomologist, Florida Dept of Agriculture & Consumer Services
Virginia Cooperative Extension
: A good article about widow spiders.
: Part of a discussion about medically significant spiders, a whole page dedicated solely to Widows.
: Part of a great website about spiders. This page specifically provides some good general information about Widow identification and their "lifestyle".